Titanium black dispersion, photosensitive resin composition, wafer level lens, light blocking film, method for producing the light blocking film, and solid-state image pickup element

Cross reference to related application

This application is a National Stage of International Application No. PCT/JP2010/068393, filed on Oct. 19, 2010, which claims priority from JP 2009-240546, filed on Oct. 19, 2009 and from Mar. 30, 2010 filed on JP 2010-079581 and JP 2010-079779, the contents of all of which are incorporated herein by reference in their entirety.

Technical field

The present invention relates to a titanium black dispersion, a photosensitive resin composition, a wafer level lens, a light-shielding film and a method for producing the same, and a solid-state image pickup device.

Background art

In recent years, small and thin image pickup units are installed on portable terminals of electric devices such as cellular phones or personal digital assistants (PDAs). Such image pickup units generally include a solid-state image pickup device such as a charge coupled device (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor and a lens that forms a subject image on the solid-state image pickup device.

Due to downsizing and thinning of portable terminals and popularization of portable terminals, image pickup units mounted thereon are also requested to be downsized and thinned, and high production efficiency is also requested. In response to these requests, a method for mass production of image pickup units is known, whereby a lens substrate on which plural lenses are formed is integrally combined with a sensor substrate on which plural solid-state image pickup devices are formed, and thereafter the lens substrate and the sensor substrate are cut such that each of the cut pieces includes a lens and a solid-state image pickup device. Examples of other production methods include: a method for producing an image pickup unit whereby only lenses are formed on a glass wafer or the like, which is then cut into a size appropriate for combined use with an individual sensor, and then combined with an image pickup device provided on a sensor substrate that has been cut into an appropriate size in advance; a method whereby plural lenses are formed from a resin by using a die, the formed lenses are attached to a sensor substrate, and the substrate is cut; a method for producing image pickup units whereby a lens substrate is cut into a size for combination with an individual sensor, and the cut pieces are combined with an image pickup device provided on a sensor substrate that has been cut into an appropriate size in advance.

Examples of known wafer level lens arrays include those having plural lenses obtained by dripping a curable resin material onto a surface of parallel flat plate substrates formed from a light-transmitting material such as glass and curing the resin material in a state in which the resin material is molded in a predetermined shape in a die (for example, see Japanese Patent No. 3926380 and the pamphlet of International Publication WO2008/102648). In some cases, light-shielding regions formed by a black film, a metal film or the like are formed at areas, other than lens portions, of the wafer level lens, or on a part of lens, in order to control the amount of light. The light-shielding region is generally formed by applying a curable light-shielding composition or depositing a metal.

Other examples of known wafer level lens arrays include a wafer level lens array obtained by forming plural through-holes through a silicon substrate, disposing a separately-formed spherical lens material at each through-hole, adhering the lens material to the substrate by soldering, and further polishing the lens material to form plural lenses (see the specification of U.S. Pat. No. 6,426,829). The lenses obtained by this production method may be provided with a light-shielding region formed by a black film, a metal film or the like similar to the above in order to control the amount of light, depending on the case.

Formation of the light-shielding region by metal deposition has problems in that the processes are complicated, lenses bend after the deposition, or scattering of light occurs due to reflection by the metal light-shielding film; accordingly, improvement is desired from the viewpoints of both of production efficiency and performance.

There are cases in which a photosensitive resin composition (light-shielding composition) in which a carbon black for use in, for example, a black matrix of a LCD is used is applied in order to impart light-shielding property.

Further, a light-shielding film is provided on a solid-state image pickup device such as a charge coupled device (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor for the purpose of noise prevention and image quality improvement.

Examples of known compositions for forming light-shielding films for solid-state image pickup devices include a photosensitive resin composition that contains a black colorant such as carbon black or titanium black.

Specifically, photosensitive resin compositions that contain titanium black having a specific X-ray diffraction peak intensity ratio, and that aims at improvement of optical density (for example, see Japanese Patent No. 3724269 and pamphlet of International Publication WO2005/037926), and photosensitive resin compositions that contain titanium black having a specific nitrogen concentration or a specific crystalline diameter (for example, see Japanese Patent Application Laid-open (JP-A) No. 2006-182627, JP-A No. 2006-206891 and JP-A No. 2006-209102) are disclosed.

Further, a composition for forming a light-shielding film that contains titanium black and a resin component, and that aims at obtainment of high light-shielding property with a small film thickness is disclosed (for example, see JP-A No. 2007-115921).

Summary of invention

Technical Problem

When conventional light-shielding compositions are used for formation of light-shielding regions (light-shielding films) in wafer level lenses, residues generated during formation of the light-shielding films tend to remain on or in the vicinity of lenses. The residues cause problems such as deterioration of the light transmittance of the lenses, which have not been mitigated yet.

A first aspect of the present invention aims at achievement of the following objects.

That is, an object of the first aspect is to provide a photosensitive resin composition for a wafer level lens which is used for formation of a light-shielding film provided in a wafer level lens, and which has excellent curability, and which is capable of decreasing photosensitive composition-derived residues in a region other than regions in which a light-shielding film is formed, and a titanium black dispersion for a wafer level lens for use in the photosensitive resin composition.

Another object of the first aspect is to provide a wafer level lens that can suppress scattering or decrease in transmittance of light in the vicinity of the light-shielding film, and a solid-state image pickup device provided with the wafer level lens.

A second aspect of the present invention aims at achievement of the following objects.

That is, an object of the second aspect is to provide a photosensitive resin composition for a wafer level lens which is used for formation of a light-shielding film provided in a wafer level lens, and which is capable of decreasing photosensitive composition-derived residues in a region other than regions in which a light-shielding film is formed, and a titanium black dispersion for a wafer level lens for use in the photosensitive resin composition.

Another object of the second aspect is to provide a wafer level lens that can suppress scattering or decrease in transmittance of light in the vicinity of the light-shielding film, and a solid-state image pickup device provided with the wafer level lens.

In recent years, due to downsizing, thinning, and sensitivity increase of solid-state image pickup devices, it has been more strongly desired that infrared light incident upon a silicon substrate, which has an image pickup device section on one side thereof, from the other side of the silicon substrate be shielded.

The reason therefor is that the silicon substrate, which is a base body of a solid-state image pickup device, exhibits high transmittance to infrared light, and that the image pickup device provided in the solid-state image pickup device exhibits sensitivity not only to visible light but also to infrared light.

Under these circumstances, a light-shielding film in which carbon black is used cannot sufficiently meet these requests since the light-shielding film has high transmittance to infrared light. In contrast, a light-shielding film in which titanium black is used has low transmittance to infrared light and excellent ability to shield against infrared light, thus being favorable as a light-shielding film that satisfies the above requests.

However, a study carried out by the present inventor clarified that formation of a light-shielding film using a titanium black-containing dispersion or a titanium black-containing photosensitive resin composition tends to leave residues derived from the photosensitive resin composition in a region other than regions in which the light-shielding film is formed.

A third aspect of the present invention aims at achievement of the following objects.

That is, an object of the third aspect is to provide a photosensitive resin composition with which a light-shielding film having excellent ability to shield against infrared light can be formed, and residues in a region other than regions in which the light-shielding film is formed is decreased when the light-shielding film is formed, and a titanium black dispersion for use in the photosensitive resin composition.

Another object of the third aspect is to provide a light-shielding film having excellent ability to shield against infrared light, and a method for producing a light-shielding film whereby a light-shielding film having excellent ability to shield against infrared light can be formed, and residues in a region other than regions in which the light-shielding film is formed is decreased when the light-shielding film is formed.

Yet another object of the third aspect is to provide a solid-state image pickup device in which noise due to infrared light is decreased, and noise due to residues is also decreased.

Solution to Problem

Means for solving the problems of the first aspect are as follows.

<1> A titanium black dispersion for a wafer level lens including titanium black particles, a dispersant, and an organic solvent, wherein 90% or more of dispersed objects that consist of the titanium black particles have particle diameters of 30 nm or less.

<2> A photosensitive resin composition for a wafer level lens including the titanium black dispersion according to <1>, a photopolymerizable compound, and a photopolymerization initiator.

<3> A wafer level lens including, at a peripheral portion of a lens present on a substrate, a light-shielding film obtained by curing the photosensitive resin composition according to <2>.

<4> A solid-state image pickup device including the wafer level lens according to <3>.

Means for solving the problems of the second aspect are as follows.

<5> A titanium black dispersion for a wafer level lens including titanium black particles, a dispersant, and an organic solvent, wherein dispersed objects including titanium black particles contain Si atoms, and the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects is 0.05 or higher.

<6> A photosensitive resin composition for a wafer level lens including the titanium black dispersion according to <5>, a photopolymerizable compound, and a photopolymerization initiator.

<7> A wafer level lens including, at a peripheral portion of a lens present on a substrate, a light-shielding film obtained by curing the photosensitive resin composition according to <6>.

<8> A solid-state image pickup device including the wafer level lens according to <7>.

Means for solving the problems of the third aspect are as follows.

<9> A titanium black dispersion including titanium black particles, a dispersant, and an organic solvent, wherein 90% or more of dispersed objects that consist of the titanium black particles have particle diameters of 30 nm or less, and the titanium black dispersion is used for formation of a light-shielding film that is provided on one side of a silicon substrate having an image pickup device section on the other side thereof, and that shields against infrared light.

<10> The titanium black dispersion according to <9>, wherein the dispersant is a graft copolymer having a graft chain in which the number of atoms excluding hydrogen atoms is from 40 to 10000.

<11> The titanium black dispersion according to <10>, wherein the graft copolymer contains at least a structural unit represented by any one of the following Formulae

to (5):

##str00001##

wherein, in Formulae

to (5), X.sup.1, X.sup.2, X.sup.3, X.sup.4, X.sup.5, and X.sup.6 each independently represent a hydrogen atom or a monovalent organic group; Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4, and Y.sup.5 each independently represent a divalent linking group; Z.sup.1, Z.sup.2, Z.sup.3, Z.sup.4, and Z.sup.5 each independently represent a monovalent organic group; R represents a hydrogen atom or a monovalent organic group; and R's having different structures may be used in mixture in the copolymer; n, m, p, q, and r each represent an integer of 1 to 500; and j and k each independently represent an integer of 2 to 8.

<12> The titanium black dispersion according to <11>, wherein the graft copolymer contains a structural unit represented by any one of Formulae

to

in a range of from 10% by mass to 90% by mass relative to the total mass of the graft copolymer.

<13> A photosensitive resin composition including the titanium black dispersion according to any one of <9> to <13>, a photopolymerizable compound, and a photopolymerization initiator, wherein the photosensitive resin composition is used for formation of a light-shielding film that is provided on one side of a silicon substrate having an image pickup device section on the other side thereof, and that shields against infrared light.

<14> A light-shielding film formed on one side of a silicon substrate having an image pickup device section on the other side thereof using the photosensitive resin composition according to <13>.

<15> A method for producing a light-shielding film including:

applying the photosensitive resin composition according to <13> to one side of a silicon substrate having an image pickup device section on the other side thereof to form a photosensitive layer;

patternwise exposing the photosensitive layer to light; and

developing the photosensitive layer after exposure to form a pattern.

<16> A solid-state image pickup device including the light-shielding film according to <14> on the one side of the silicon substrate having an image pickup device section on the other side thereof.

<17> The solid-state image pickup device according to <16> including:

the silicon substrate having the image pickup device section on the other side thereof;

a metal electrode provided on the one side of the silicon substrate and electrically connected to the image pickup device section; and

the light-shielding film according to <14> provided on the side of the silicon substrate on which the metal electrode is provided, and patterned to expose at least a part of the metal electrode.

<18> The solid-state image pickup device according to <16>, further including a metal electrode provided on the one side of the silicon substrate and electrically connected to the image pickup device section, the light-shielding film being patterned to expose at least a part of the metal electrode.

Advantageous Effects of Invention

According to the first aspect, it is possible to provide a photosensitive resin composition for a wafer level lens which is used for formation of a light-shielding film provided in a wafer level lens, and which has excellent curability, and which is capable of decreasing photosensitive composition-derived residues in a region other than regions in which a light-shielding film is formed, and a titanium black dispersion for a wafer level lens for use in the photosensitive resin composition.

According to the first aspect, it is also possible to provide a wafer level lens that can suppress scattering or decrease in transmittance of light in the vicinity of the light-shielding film, and a solid-state image pickup device provided with the wafer level lens.

According to the second aspect, it is possible to provide a photosensitive resin composition for a wafer level lens which is used for formation of a light-shielding film provided in a wafer level lens, and which is capable of decreasing photosensitive composition-derived residues in a region other than regions in which a light-shielding film is formed, and a titanium black dispersion for a wafer level lens for use in the photosensitive resin composition.

According to the second aspect, it is also possible to provide a wafer level lens that can suppress scattering or decrease in transmittance of light in the vicinity of the light-shielding film, and a solid-state image pickup device provided with the wafer level lens.

According to the third aspect, it is possible to provide a photosensitive resin composition with which a light-shielding film having excellent ability to shield against infrared light can be formed, and residues in a region other than regions in which the light-shielding film is formed is decreased when the light-shielding film is formed, and a titanium black dispersion for use in the photosensitive resin composition.

According to the third aspect, it is also possible to provide a light-shielding film having excellent ability to shield against infrared light, and a method for producing a light-shielding film whereby a light-shielding film having excellent ability to shield against infrared light can be formed, and residues in a region other than regions in which the light-shielding film is formed is decreased when the light-shielding film is formed.

According to the third aspect, it is also possible to provide a solid-state image pickup device in which noise due to infrared light is decreased, and noise due to residues is also decreased.

Brief description of drawings

FIG. 1 is a plan view showing an example of a wafer level lens array.

FIG. 2 is a cross-sectional view taken along the line A-A shown in FIG. 1.

FIG. 3 is a view showing a state in which a molding material for forming a lens is supplied onto a substrate.

FIGS. 4A to 4C are schematic views showing a procedure of forming lenses on a substrate using a mold.

FIGS. 5A to 5C are schematic views showing a process of forming a patterned light-shielding film on a substrate on which lenses have been formed.

FIG. 6 is a cross-sectional view showing an example of a wafer level lens array.

FIGS. 7A to 7C are schematic views showing another embodiment of a process of forming a light-shielding film.

FIGS. 8A to 8C are schematic views showing a process of forming a lens on a substrate having a patterned light-shielding film.

FIG. 9 is a schematic cross-sectional view illustrating a configuration of a camera module equipped with a solid-state image pickup device according to one example of the third embodiment.

FIG. 10 is a schematic cross-sectional view illustrating a solid-state image pickup device according to one example of the third embodiment.

FIG. 11 is a schematic cross-sectional view of a substrate 3A used in Example 3-2 and Comparative Example 3-2.

FIG. 12 is a schematic cross-sectional view illustrating a state in which a light-shielding film is formed on a substrate 3A.

FIG. 13 is a schematic cross-sectional view of a substrate 3B used in Example 3-3 and Comparative Example 3-3.

FIG. 14 is a schematic cross-sectional view illustrating a state in which a light-shielding film is formed on a substrate 3B.

Description of embodiments

In the following, a titanium black dispersion for a wafer level lens, a photosensitive resin composition including the same, and a wafer level lens according to a first embodiment, and a titanium black dispersion for a wafer level lens, a photosensitive resin composition including the same, and a wafer level lens according to a second embodiment, and a titanium black dispersion and photosensitive resin composition according to a third embodiment are described in detail.

"Wafer level lens" as used herein means a lens which is provided in an image pickup unit (for example, a solid-state image pickup device) and comprises an individual lens present on a substrate and a light-shielding film provided at a peripheral portion of the lens. A group of such wafer level lenses is referred to as "wafer level lens array".

<Titanium Black Dispersion for Wafer Level Lens and Photosensitive Resin Composition Including the Same According to First Embodiment>

The titanium black dispersion for a wafer level lens of the first embodiment (hereinafter sometimes simply referred to as "titanium black dispersion") is a dispersion that includes titanium black particles, a dispersant, and an organic solvent, wherein 90% or more of dispersed objects that consist of the titanium black particles have particle diameters of 30 nm or less.

The photosensitive resin composition for a wafer level lens of the first embodiment (hereinafter sometimes simply referred to as "photosensitive resin composition") is a photosensitive resin composition that includes the titanium black dispersion of the first embodiment, a photopolymerizable compound, and a photopolymerization initiator.

The titanium black dispersion and the photosensitive resin composition of the first embodiment are used for formation of a light-shielding film of a wafer level lens.

Respective components contained in the titanium black dispersion or photosensitive resin composition of the first embodiment are described below in order.

--Titanium Black Particles of First Embodiment--

The titanium black dispersion of the first embodiment includes titanium black particles. The titanium black particles are contained as dispersed objects in the dispersion, and, in the first embodiment, 90% or more of dispersed objects that consist of titanium black particles have particle diameters of 30 nm or less. That is, 90% or more (in terms of particle number) of dispersed titanium black particles have particle diameters of 30 nm or less.

The diameter of a dispersed object in the first embodiment means the particle diameter of the dispersed object, and the particle diameter is the diameter of a circle having the same area as the projection area of the outer surface of the particle. The projection area of a particle can be obtained by measuring the area thereof obtained by taking an electron micrograph, followed by correction for the magnification of the electron micrograph.

Here, the "dispersed objects that consist of titanium black particles" in the first embodiment encompasses titanium black particles in the form of primary particles as well as titanium black particles in the form of aggregates (secondary particles).

The photosensitive resin composition of the first embodiment includes dispersed objects that consist of titanium black particles derived from the titanium black dispersion of the first embodiment. 90% or more of the dispersed objects that consist of titanium black particles and that are contained in the photosensitive resin composition and in a cured film (a light-shielding film) obtained by curing the photosensitive resin composition have particle diameters of 30 nm or less.

In the first embodiment, since 90% or more of the dispersed objects that consist of titanium black particles have particle diameters of 30 nm or less, residues derived from the photosensitive composition in a region other than regions in which the light-shielding film is formed is reduced when a light-shielding film is formed using the photosensitive resin composition of the first embodiment. Here, the residues include components derived from the photosensitive composition, such as titanium black particles and resin components.

Although the reason why the residues are decreased is still unclear, it is presumed that dispersed objects having small diameters contribute to improvement in removability of uncured photosensitive resin composition (in particular, titanium black particles) during the formation of a light-shielding film.

In addition, since titanium black particles have excellent light-shielding property to light of a wide range of wavelength regions ranging from ultraviolet to infrared, the light-shielding film formed using the titanium black dispersion or photosensitive resin composition of the first embodiment exhibits excellent light-shielding property.

In order to determine whether or not 90% of the dispersed objects contained in the titanium black dispersion or photosensitive resin composition of the first embodiment have particle diameters of 30 nm or less, the following method (1-1) is employed.

In order to determine whether or not 90% of the dispersed objects contained in the cured film (light-shielding film) obtained by curing the photosensitive resin composition of the first embodiment have particle diameters of 30 nm or less, the following method (1-2) is employed.

<Method (1-1)>

The titanium black dispersion or photosensitive resin composition is diluted 500-fold with propylene glycol monomethyl ether acetate (hereinafter sometimes simply referred to as "PGMEA"), and dripped onto a carbon thin film and dried, and a photograph for morphological observation is taken using a transmission electron microscope. The projection areas of the outer surfaces of 400 particles are determined from the obtained photograph, the diameters of circles corresponding to the areas are calculated, and the frequency distribution thereof is evaluated.

<Method (1-2)>

A photograph for morphological observation and elemental maps for Ti and Si of a cross-section of the film-formed substrate is taken using a scanning electron microscope (S-3400N (trade name) manufactured by Hitachi High-Technologies Corporation), and an energy-dispersive X-ray analyzer (GENESIS (trade name) manufactured by EDAX Inc.). The projection areas of the outer surfaces of 400 particles in which Ti element has been detected are determined from the obtained photograph, the diameters of circles corresponding to the areas are calculated, and the frequency distribution thereof is evaluated.

<Titanium Black Dispersion for Wafer Level Lens and Photosensitive Resin Composition Including the Same According to Second Embodiment>

The titanium black dispersion for a wafer level lens of a second embodiment (hereinafter sometimes simply referred to as "titanium black dispersion") includes titanium black particles, a dispersant, and an organic solvent, and dispersed objects including the titanium black particles contain Si atoms, and the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects is 0.05 or higher.

In addition, the photosensitive resin composition for a wafer level lens of the second embodiment (hereinafter sometimes simply referred to as "photosensitive resin composition") is a photosensitive resin composition that includes the titanium black dispersion of the second embodiment, a photopolymerizable compound, and a photopolymerization initiator.

That is, the photosensitive resin composition of the second embodiment includes titanium black particles, a dispersant, and an organic solvent, which are components of the titanium black dispersion of the second embodiment, and further includes a photopolymerizable compound and a photopolymerization initiator; Further, the dispersed objects, including the titanium black particles, contain Si atoms, and the content ratio of Si atoms to Ti atoms (Si/Ti; weight/weight, the same applies hereinafter) in the dispersed objects is 0.05 or higher.

The titanium black dispersion and the photosensitive resin composition of the second embodiment are used for formation of a light-shielding film in a wafer level lens.

Respective components contained in the titanium black dispersion or photosensitive resin composition of the second embodiment are described below in order.

--Titanium Black Particles of Second Embodiment--

The titanium black dispersion of the second embodiment includes titanium black particles. The titanium black particles are contained as dispersed objects in the dispersion. In the second embodiment, the dispersed objects, including titanium black particles, contain Si atoms, and the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects is 0.05 or higher.

Here, the "dispersed objects including titanium black particles" in the second embodiment encompasses a case in which titanium black particles are in the form of primary particles and a case in which titanium black particles are in the form of aggregates (secondary particles).

When the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects of the second embodiment is higher than 0.5, preparation of a pigment dispersion using the dispersed objects is difficult. Accordingly, the upper limit of the content ratio is preferably 0.5.

An excessively low Si/Ti of the dispersed objects tends to cause residues at removal regions when a light-shielding film in which the dispersed objects in the second embodiment are used is patterned by, for example, photolithography. An excessively high Si/Ti of the dispersed objects decreases the ability to shield against light. Therefore, Si/Ti of the dispersed objects is more preferably from 0.05 to 0.5, and even more preferably from 0.07 to 0.4.

The following means may be employed in order to provide a Si/Ti of the dispersed objects of 0.05 or higher.

Titanium black having a Si/Ti of the dispersed objects of 0.05 or higher can be obtained by dispersing titanium oxide and silica particles by using a disperser to obtain a dispersion, and subjecting the resultant mixture to reducing treatment at high temperature.

Here, a specific embodiment for providing a Si/Ti of the dispersed objects of 0.05 or higher is explained.

Titanium black having a Si/Ti of 0.05 or higher can be prepared by, for example, a method described in the paragraphs [0005]

and

to

of JP-A No. 2008-266045.

The photosensitive resin composition of the second embodiment includes dispersed objects that consist of titanium black particles derived from the titanium black dispersion of the second embodiment. The dispersed objects, including titanium black particles, contained in the photosensitive resin composition and in the cured film (light-shielding film) obtained by curing the photosensitive resin composition also have the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects of 0.05 or higher, and preferable ranges thereof are also the same as those described above.

In the second embodiment, since the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects including titanium black particles is 0.05 or higher, residues derived from the photosensitive composition in a region other than regions in which the light-shielding film is formed are reduced when a light-shielding film is formed using the photosensitive resin composition of the second embodiment containing the dispersed objects. The residues include components derived from the photosensitive composition, such as titanium black particles and resin components.

Although the reason why the residues are reduced is still unclear, it is presumed that the dispersed objects tend to have small particle diameters (for example, particle diameters of 30 nm or less), and an increase in the proportion of Si atom-containing components in the dispersed objects decreases adsorptivity of the entire film to an underlying support, as a result of which the photosensitive resin composition of the second embodiment including the dispersed objects has improved development removability of an uncured photosensitive resin composition (in particular, titanium black particles) during the formation of a light-shielding film.

In addition, since titanium black particles have excellent light-shielding property to light in a wide range of wavelength regions ranging from ultraviolet to infrared, the light-shielding film formed using the titanium black dispersion or photosensitive resin composition of the second embodiment exhibits an excellent light-shielding property.

In order to determine whether or not the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects contained in the titanium black dispersion or photosensitive resin composition of the second embodiment is 0.05 or higher, the following method (2-1) is employed.

<Method (2-1)>

The titanium black dispersion or photosensitive resin composition is subjected to heating treatment under an oxygen atmosphere, and dispersed objects including titanium black particles are taken out.

20 mg of the titanium black dispersion or photosensitive resin composition is weighed out, 0.1 mL of HF, 1 mL of HNO.sub.3 (10% aq.), 1 mL of H.sub.2SO.sub.4 (5% aq.), and 1 mL of HCl (3% aq.) are added thereto and subjected to microwave dissolution. At this time, the temperature of the liquid is 180.degree. C.

Then, H.sub.2O is added to this mixture solution until the total volume reached 100 ml, and the resultant mixture is subjected to ICP-OES (ATTOM (trade name), manufactured by SII Co., Ltd.) to carry out an elemental analysis. The mass ratio of Si/Ti is calculated from the results obtained.

In order to determine whether or not the content ratio of Si atoms to Ti atoms (Si/Ti) in the dispersed objects contained in the cured film (light-shielding film) obtained by curing the photosensitive resin composition of the second embodiment is 0.05 or higher, the following method (2-2) is employed.

<Method (2-2)>

A substrate on which the light-shielding film is formed is split to prepare a cross-section of the light-shielding film, and the cross-section is measured with an energy-dispersive X-ray fluorescence spectrometer, as a result of which the amount of Si atoms and the amount of Ti atoms at a surface of the light-shielding film can be obtained. The ratio therebetween is evaluated as Si/Ti in the light-shielding film.

Here, energy-dispersive X-ray fluorescence spectroscopy can be carried out using, for example, S-4800 (trade name) manufactured by Hitachi High-Technologies Corporation as a scanning electron microscope and an INCA ENERGY PENTAFETX3 (trade name) manufactured by Oxford Corp. as an energy-dispersive X-ray fluorescence detector.

In addition, a measurement method using an energy-dispersive X-ray fluorescence spectrometer may be used not only for measurement of the content ratio of Si atoms to Ti atoms in the dispersed objects contained in the cured film (light-shielding film), but also for measurement of the content ratio of Si atoms to Ti atoms in powder. Therefore, the content ratio of Si atoms to Ti atoms of the dispersed objects contained in the titanium black dispersion or photosensitive resin composition can be measured by carrying out energy-dispersive X-ray fluorescence spectroscopy on a powder obtained by, for example, heating the titanium black dispersion or photosensitive resin composition. The measurement may be carried out according to the following method (2-3).

<Method (2-3)>

The titanium black dispersion or photosensitive resin composition is heated to 700.degree. C. under an oxygen atmosphere using a small rotary kiln (manufactured by Motoyama Co., Ltd.) and maintained in that state for 30 minutes and then cooled to obtain 2 g of powder. The powder obtained is placed on a tungsten plate having a thickness of 0.2 mm, the plate is placed in a vacuum chamber equipped with an electron beam heating mechanism and subjected to heating treatment at 1000.degree. C. for 30 seconds by electron beam heating at a degree of vacuum of 10.sup.-5 Torr or less. The Si/Ti ratio is calculated by obtaining the amount of Si atoms and the amount of Ti atoms of the powder, which has been subjected to the heating treatment, by using a field emission scanning electron microscope S-4800 (trade name, manufactured by Hitachi High-Technologies Corporation) and an energy-dispersive X-ray fluorescence detector INCA Energy PentaFETx3 (trade name, Manufactured by Oxford Corp.).

<Titanium Black Dispersion and Photosensitive Resin Composition of Third Embodiment>

The titanium black dispersion of the third embodiment is a titanium black dispersion for use in formation of a light-shielding film which is provided on one side of a silicon substrate having an image pickup device section on the other side thereof and which shields against infrared light, the titanium black dispersion including titanium black particles, a dispersant and an organic solvent, wherein 90% or more of the dispersed objects that consist of titanium black particles have particle diameters of 30 nm or less. That is, 90% or more (in terms of particle number) of dispersed titanium black particles have particle diameters of 30 nm or less.

In addition, the photosensitive resin composition of the third embodiment is a photosensitive resin composition that includes the titanium black dispersion of the third embodiment, a photopolymerizable compound, and a photopolymerization initiator, and is used for formation of a light-shielding film which is provided on one side of a silicon substrate having an image pickup device section on the other side thereof and which shields against infrared light.

In recent years, due to downsizing, thinning, and increase in sensitivity of solid-state image pickup devices, there is an increasing request that, in a silicon substrate having an image pickup device section on one side thereof (hereinafter also referred to as "first main face" or "front side"), infrared light incident upon the silicon substrate from the other side thereof (hereinafter, referred to as "second main face" or "back side") be shielded. The light-shielding film in which titanium black is used has excellent ability to shield against infrared light, thus being favorable as a light-shielding film satisfying the request.

However, as a result of study on the third embodiment, it has been found that, when a light-shielding film is formed using a dispersion or photosensitive resin composition that includes titanium black, residues derived from the photosensitive resin composition tend to be left in a region other than regions in which the light-shielding film is formed. Although the reason why the residues tend to be left is not clear, it is presumed that tendency for titanium black particles to precipitate over time, tendency for titanium black particles to become coarse, etc. have relation therewith.

Accordingly, as a result of further research of the third embodiment, it has been found that the residues can be reduced while maintaining the ability of titanium black to shield against infrared light, by forming a light-shielding film by using the titanium black dispersion or photosensitive resin composition in which 90% or more of the dispersed objects that consist of titanium black particles have particle diameters of 30 nm or less, and thus the third embodiment has been completed.

Thus, with the titanium black dispersion and photosensitive resin composition of the third embodiment, a light-shielding film having excellent ability to shield against infrared light can be formed, and residues in a region other than regions in which the light-shielding film is formed can be reduced during formation of the light-shielding film.

Here, "infrared" means a wavelength region of from 700 nm to 1200 nm.

The description continues in the full USPTO document.